This invention relates generally to medical devices for the drainage of fluids, and more specifically to ureteral stents.
A ureter is a tubular passageway in a body that conveys urine from a kidney to a bladder. Urine is transported through the ureter under the influence of hydrostatic pressure, assisted by contractions of muscles located within the walls (lining) of the ureter. Some patients experience a urological condition known as ureteral blockage or obstruction. Some common causes of ureteral blockage are the formation of tumors or abnormalities within the ureteral lining, or the formation and passage of kidney stones.
Ureteral stents are used to facilitate urinary drainage from the kidney to the bladder in patients having a ureteral obstruction or injury, or to protect the integrity of the ureter in a variety of surgical manipulations. Stents may be used to treat or avoid ureter obstructions (such as ureteral stones or ureteral tumors) which disrupt the flow of urine from the kidneys to the bladder. Serious obstructions may cause urine to back up into the kidneys, threatening renal function. Ureteral stents may also be used after endoscopic inspection of the ureter.
Ureteral stents typically are tubular in shape, terminating in two opposing ends: a kidney distal end and a bladder proximal end. One or both ends of a ureteral stent may be coiled in a spiral, pigtail or hook-type J-shape to prevent the upward and/or downward migration of the stent due, for example, to physiological movements. A kidney end coil is designed to retain the stent within the renal pelvis and to prevent stent migration down the ureter. The bladder end coil sits in the bladder and is designed to prevent stent migration upward toward the kidney. The bladder coil is also used to aid in retrieval and removal of the stent.
Unfortunately, certain drawbacks are inherent with these types of ureteral stents. For example, the extraneous material associated with the coiled ends of the stent can be an irritant to the patient, particularly in the trigone area. This trigonal irritation can be exacerbated, for example, by kidney motion relative to stent placement. Even normal breathing activity of a patient can result in significant kidney motion, on the order of 2-4 centimeters, resulting in irritation and discomfort for the patient.
What is needed is a ureteral stent with a bladder end design and connection method that prevents stent migration towards the kidney, does not irritate the trigone area of the bladder, does not create patient discomfort during routine motion of the bladder or kidney, and that prevents urine reflux up the ureter during bladder voiding.
One aspect of the present invention is directed to an expandable ureteral stent comprising an elongated member, a proximal retention structure, and a resilient portion connecting them. Each of these has a lumen, the lumens being in fluid communication with each other. The resilient portion allows the proximal retention structure to slideably move in relation to the proximal end of the elongated member between an expanded position and a retracted position.
In embodiments of the invention, the retention structure can comprise a nonlinear shape, a horn shape, a spherical shape, a mushroom shape, or a flared shape. The outer dimension of the proximal retention structure is larger than the outer diameter of the elongated member, to prevent entry of the proximal retention structure into the intramural tunnel.
In another embodiment, a stricture is disposed within one of the lumens to minimize urine reflux. The stricture can comprise an orifice in the proximal retention structure.
The resilient portion can comprise an elastomeric sleeve. The elastomeric sleeve can be disposed internally or externally relative to the elongated member. Additionally, it can be partially contained within the lumen of the elongated member when the proximal retention structure is in a retracted position. The resilient portion can also comprise a spring, and the spring can be biased toward the retracted position of the stent. The spring can be integrally formed with the proximal retention structure.
In some embodiments of the invention, the proximal retention structure is slideably moveable within the lumen of the elongated member. A retaining device can be used to prevent separation of the proximal retention structure and the elongated member. This retaining device can be a circumferential flange.
In some embodiments the stent comprises a distal retention structure. This distal retention structure defines a lumen, which is in fluid communication with the lumen of the elongated member. There can be an opening in the distal retention structure to allow drainage into its lumen.
In yet another aspect, the invention features an apparatus for positioning a ureteral stent having a retention structure with a nonlinear shape and a resilient portion, the apparatus comprising a guide wire and a pusher. The shape of the distal end of the pusher conforms to the shape of the retention structure of the stent, which can be a nonlinear shape, a horn shape, a spherical shape, a mushroom shape, or a flared shape. The pusher travels along the guide wire. The guide wire passes through the resilient portion of the stent.
In another aspect, the invention features a method of facilitating urinary drainage from a kidney to a bladder in a patient that reduces discomfort to the patient, comprising positioning a ureteral stent having an elongated member, a retention structure, and a resilient portion in the ureter of a a patient, and allowing the retention structure to slideably move relative to the elongated member, based on positioning of organs with the patient, including the kidney and bladder, or the breathing pattern of the patient. The resilient portion can be biased to a retracted position.
Another aspect of the invention features a method of manufacturing an adjustable stent. This comprises the steps of providing an elongated member, a retention structure and a resilient portion, and connecting the elongated member and the retention structure to opposing ends of the resilient portion. The resilient portion can include a coiled spring, which can be formed by an extrusion process. Heat forming techniques can be used to connect the resilient portion, or it can be integrally formed with the elongated member or the retention structure. A circumferential flange can be used to retain the spring.